A Mössbauer investigation of the hydrogenation of the Nd2Fe14B phase during hydro/solvothermal recycling process applied to Nd-Fe-B magnets

Nd-Fe-B magnets submitted to hydrothermal and solvothermal recycling processes were investigated by Mössbauer spectrometry. Both treatments lead to the hydrogenation of the Nd 2 Fe 14 B magnetic phase into Nd 2 Fe 14 BH x , with a hydrogen content x that was determined by X-ray diffraction. The Mössbauer spectrum of the Nd 2 Fe 14 BH x phase was characterized by comparison with that of the non hydrogenated Nd 2 Fe 14 B phase. It was shown that the mean hyperfine field of the Nd 2 Fe 14 BH x phase increases with the hydrogen content x. The increase of the mean hyperfine field can be related to the increase of the Nd 2 Fe 14 BH x unit cell volume. These results show that the hydrogen content of the Nd 2 Fe 14 BH x phase can be estimated by Mössbauer spectrometry. • Nd-Fe-B magnets submitted to hydrothermal and solvothermal recycling processes were investigated by Mössbauer spectrometry. • Both treatments lead to the hydrogenation of the Nd 2 Fe 14 B magnetic phase into Nd 2 Fe 14 BH x . • The mean hyperfine field of the Nd 2 Fe 14 BH x phase increases with the hydrogen content x, with a more pronounced increase for x < 1. • This tendency is the same as that observed in the literature for the Curie temperature of the Nd 2 Fe 14 B phase hydrogenated by heating Nd-Fe-B alloys in hydrogen atmosphere. • Mössbauer spectrometry allows estimating the hydrogen content of the Nd 2 Fe 14 BH x phase.